Method of making cold shaped polymerized articles



Dec. 11, 1945. w. E. WILLIAMS 7 2,390,567

METHOD OF MAKING COLD SHAPED POLYMERIZED ARTICLE Filed March 13, 1945 2Sheets-Sheet 1 INVENTOR WILLIAM EWHRT WILYLIHMS BY v/m @TORNEY Dec. 11,1945. w. E. WILLIAMS 9 I METHOD OF MAKING COLD SHAPED POLYMERIZEDARTICLE Filed March 13, 1943 2 Sheets-Sheet 2 INVENTOR WILLIAM EWHRTwlLunMs V Patented Dec. 11, 1945 V UNITE Sr 3 ENT or METIHUD OF G COLDSHAPED POLYMERIZED ARTICLES William Ewart Williams, Pasadena, Calif.

Application March 13, 1943, Serial No -179,052

6 Claims.

structure characterized by relatively weak cross- I linkages, whichcross-linkages in the original material are still further weakened bychemical means, without appreciably destroying the said chain-likestructure, so that this modified material may be bent, formed, molded orotherwise manipulated to any desired shapes at substantially ordinaryroom temperatures and then the original cross-linkage restored to itsformer condition and to such new treated material and to new andimproved processes of accomplishing these results.

This application is a continuation in part of my copending applicationSerial Number 375,000, filed January 18, 1941.

v The principal object of this invention is to provide a method offorming articles without internal stress, strain or other irregularitiesthus substantially eliminating the tendency to return to their originalshape or become deformed.

Another object of the'invention is to provide a method of forming apolymerized article which has been chemically treated so that it may bebent to any desired shape at substantially room temperature.

Another object of the invention is to provide a method of obtaining atreated polymerized material which is of such a nature that it may bereshaped without heat.

Another object Of the invention is to provide new and improved chemicalprocesses for modifyingthe cross-linkage structure of a polymerizedmaterial.

Another object of the invention is to provide new and improved method ofcold bending polymerized material without appreciably altering itssurface texture or polish.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyindrawings. It is apparent that many changes may be made in the steps ofthe processes without departing from the invention as set forth in theaccompanying claims. Therefore, it is not desired to limit the inventionto the exact method shown and described as the preferred method has beenset forth by way of illustration only.

Referring to the drawings:

Fig. I is a face view of a strip of polymerized material;

Fig. II is a perspective view of the strip after it has been chemicallytreated and illustrating one of the shapes to which it may be formed atordinary room temperature;

Fig. III is a face view of a disk of material to be treated andreshaped;

Fig. IV is a diagrammatic sectional view illustrating a prior method ofheat shaping polymerized material to the shape of a hemisphere;

Fig. V is a view similar to Fig. III of said ma.-'

terial treated according to the present invention and shaped to ahemisphere without heat;

Fig. VI is a sectional view of a tank diagrammatically illustrating thematerial under treatment immersed in the chemical bath;

Fig. VIII is a diagrammatic cross sectional view of a heating chamber inwhich the material, which has been treated and shaped, may be heated.

Prior to my invention polymerized material has been shaped through theaction of heat which has the disadvantage of setting up intemal strainsand stresses in the shaped article which materially reduces itspermanence of form and usefulness. It is, therefore, a principal objectof my invention to provide means by which this material may be reshapedwithout the application of heat and without materially changing ordisturbing its surface texture and in which the reshaped article issubstantially free of said internal strains and stresses.

By way of illustrating the process we will take a strip of polymerizedmethyl' methacrylate i. The polymerized methyl methacrylate materialinherently has a chain-like molecular structure with relatively weakcross-linkages.

To form this material, according to the present invention, to the shapedesired, the material I! is immersed in a bath 6 of concentrated (95%approximately) hydrogen peroxide as shown in Fig.

. VI. After immersing for a number of hours at approximately 25 C., theexact time being dependent upon the size and shape of the article to beformed and upon the degree of softness desired, longer soaking producinggreater softening, the material I isremoved fromthe bath and is thenshaped or molded as desired when cold, as diagrammatically illustratedin Figs. II and V. At this temperature the material is soft and plasticand in a stage something between that of ordinary para rubber and puttyso that its molding or I forming can be carried out with a very smallamount of force. If it be retained in this shape and warmed up toapproximately 40 C. the material can be transformed in a few hours backto the original material but it will have the new desired shape withoutappreciable strain.

The material may be heated or warmed by placing it in a suitable heatingdevice, such as illustrated in Fig. VII. The said device has a chamher Iheated by suitable heating unit 8. In this instance the block 3 havingthe bent material 2 thereon is shown in the chamber.

One of the shapes shown by way of illustration is that of a spiral asillustrated in Fig. II of the drawings. It may be formed merely bytwisting and then by being held in said twisted position with clamps andthereafter set to this shape by restoring the material to its originalcondition. As a further example, I can transform a disk 2, such asillustrated in Fig. 111, into the modified state which can then bepulled over, for example, a spherical form 3 to give a hemisphericalshell as shown in Fig. V.

If disk of untreated material of the same size as disk 2 is heated in anoven to a temperature of about 100 to 150 C. and then formed over thehemispherical former 3 the resultant shell in this latter case, as iswell known, will be much thinner at its top d than at its lower edges 5while in my invention the corresponding reduction of thickness is verymuch less. In following the prior art of heat treating and forming thedisc 2 to the shell, such as illustrated in Fig. IV, there is aninherent tendency to introduce internal strains and stresses since thisis an elastic deformation Whereas by following the present method, asillustrated in Fig. V, a considerable amount of plastic flow is obtainedwhich materially reduces these strains and stresses and thicknessreduction is avoided.

While it is not certain, it is believed that a molecular change has beenmade in the material. What actually happens, it is believed, is that thehydrogen peroxide in effect, goes in solution in the polymerizedmaterial forming an sub chain. The material necessarily swellsappreciably and the cross-linkage originally present is veryconsiderably weakened if not entirely destroyed. When the hydrogenperoxide is removed the polymerized compound returns to its originalstate. If, after forming, the temperature of the plastic is reduced toapproximately 4 C. the formed article becomes rigid and can be removedfrom the former. main at a low temperaturefor a considerable periodduring which the peroxide slowly comes out. As the material hardens thetemperature can be raised somewhat and the hydrogen peroxide graduallydifiuses out. At the last stage it can be completely dried at about 30to 35 C. A curious modification of the methyl methacrylate can beobtained but the exact conditions of its creation have not beendetermined. In this modification, the otherwise transparent methacrylatebecomes opalescent or milky and if this stage is arrived at it can onlybe made transparent again by heating up to approximately 45 or 50 C. Ifa piece of methyl methacrylate containing the peroxide is heated toapproximately 60 to 80 C. either internal bubbles can be formed in thematerial or a real chemical change will take place at localized spotscausing a variegated appearance of the substance which may make ituseful in the production of articles for decorative purposes.

The modified material described, when reshaped under commercialprocesses, has but a It is allowed to re' i very slight tendency toreturn to the shape of the original material as compared with thepronounced tendency to do so where displacement has been made under theaction of heat.

Where the polymerized material has been com-' mercially reshaped underthe action of heat the change in the material is entirely .a. physicalchange but wher the shaping is done under my procedure it is believedthat there has been a chemical change. The fact that the polymerizationchains are not broken means that polished surfaces that were on theoriginal material are not injured.

Containers for the hydrogen peroxide used in the immersion treatmentshould be made only of Pyrex or similar forms of glass which do notcause decomposition of the hydrogen peroxide. as most metals or ordinaryglassware cause decomposition. The density of. the hydrogen peroxide isapproximately 1.4 while the density of the methyl methacrylate is about1.2. The result is that when a flat dish is used the methyl methacrylatecannot be fully immersed so it is better in practice to use narrowvertical containers and use weights or other methods of pulling thesheets down into the liquid to keepit totally immersed.

Contrary to accepted opinions inhibitors may be used successfully withhigh concentrations of hydrogen peroxide and retard the selfdecomposition very materially.

If the forming molds are made out of porous materials, such as partiallysintered glass or quartz particles, then the removal of the hydrogenperoxide can be effected without removing the formers or mold so thatthe shape can be retained until the material is rigid enough to be selfsupporting or to maintain its shape without any deformation. Anothermethod used is as follows: The article is molded between dies which maynot be necessarily porous, then cooling the dies with the material inplace to about below 10 C. and the molded article is then removed. Theresulting chilled rigid material is then placed in temporary holdingformers which are porous and the hydrogen peroxide is allowed to diffuseout of the material by means of fairly low heat treatment, about 35, 40or 45 C.

Hydrogen peroxide of the type used is disclosed in The Merck Index,fifth edition, page 2G7 and other places.

Although methyl methacrylate is set' forth above by way of illustration,it is to be understood that the present invention is intended to includeany polymerized material selected from a group comprising esters ofacrylic, methacrylic or ethyl acrylic resins, materials knowncommercially as Plexiglass and Lucite, methyl methacrylate, plasticizedmethacrylate, internally plasticized methacrylate as byco-polymerization of methyl methacrylate with alkyl methacrylates,acrylates, etc., all of which are of the type having a. chain-likemolecular structure with reladows and Windshields and the maintenance ofthe polished surfaces thereof.

Another important use is that of producing protection plastic lenses forgoggles and eye protectors for fliers,- industrial workers, andmotorcycle riders or troops, as thes lenses may be cold shaped todesired form without destruction of the polished and clear preformedoptical surfaces thereon.

This is the first instance, as far as is known, where a chemical-changeis effected in a polymerized substance without breaking up thepolymerization thereof and without materially altering the finishedsurfaces thereon.

Having described my invention, I claim:

1. The process of forming an article of polymeric methyl methacrylatecomprising treating said polymeric methyl methacrylate under controlledtemperatures for controlled times with hydrogen peroxide having aconcentration of approximately ninety-five percent in the absence ofheating until said polymeric methyl methacrylate reaches a desireddegree of softness, shaping said methyl methacrylate without heating, toa desired form, and thereafter removing the hydrogen peroxide from themethyl methacrylate by evaporation.

2. The process of forming an article of polymeric methyl methacrylate inthe absence of heating, comprising treating said polymeric' methylmethacrylate under controlled temperature for a controlled time withconcentrated hydrogen peroxide, treating said polymeric methylmethacrylate until it reaches a desired degree of softness, shaping saidpolymeric methyl methacrylate to a desired form, and thereafter removingthe hydrogen peroxide from the polymeric methyl methacrylate.

3. The process of forming an article of polymeric methyl methacrylate inthe 'absence of heating, comprising treating said polymeric methylmethacrylate under controlled temper-'- ature for a controlled time withconcentrated hydrogen peroxide, treating said methyl methacrylate untilit reaches a desired degree of softness, removing said polymeric methylmethacrylate from the presence of the concentrated hydrogen peroxide,shaping said methyl methacrylate to a desired form while still softwithout heating,

and thereafter substantially freeing the methyl methacrylate from thehydrogen peroxide.

4. The-process of forming an article of polymeric methyl methacrylate-inthe absence of heating, comprising treating said methyl methacrylateunder controlled time with a liquid bath of hydrogen peroxide until saidmethyl methacrylate reaches a desired degree of softness, removing themethyl methacrylate from the hydrogen peroxide bath, shaping said methylmethacrylate to a desired form, and thereafter removing the hydrogenperoxide from the methyl methacrylate while the methyl methacrylate isheld in the desired form.

5. The process of forming an article of a polymerized methacrylatematerial of the type having a chain-like molecular structure with weakcross-linkages comprising treating said polymerized methacrylatematerial with hydrogen peroxide tobring about a further weakening ofsaid weak cross-linkages and for a time interval of treatment sufficientto soften said material by an amount which will enable the shaping ofsaid material, shaping said material to a desired shape while in saidsoftened state and without softening by heat and thereafter substan'tia-lly restoring the cross-linkages to their original condition bysubstantially removing the' hydrogen peroxide from the polymerizedmethacrylate material.

6. The process of forming an article of a polymerized acrylate material,comprising treating the said material with highly concentrated hydrogenperoxide until the cross-linkages are substantially removed, forming thematerial without heat to the desired shape and restoring thecross-linkages by substantially removing the hydrogen peroxide from thepolymerized material.

WILLIAM EWART WILLIAMS.

